The invention relates to a method for surface treatment of fibrous polyphenylene sulfide or polysulfone. Combined into area structures, such fibers find applications as separators in electrochemical energy storage devices containing alkali electrolyte.
Electrochemical energy storage devices consist of at least one positive and one negative electrode that are surrounded by a liquid electrolyte. To avoid contact between the positive and negative electrode, and thus, to avoid an undesired current flow inside such an energy storage device, the electrodes are isolated from one another by separators without significantly impairing the passage of the electrolyte's ions.
For use as separators, fiber materials must meet the following requirements:
Resistance to electrolyte and oxidation; PA1 Close weight and thickness tolerances; PA1 Mechanical stability (at least a maximum tensile strength of 70 N/5 cm); PA1 Flexibility for a close fit at the electrodes; PA1 Immediate wettability (less than 10 sec) through the Respective electrolyte; and PA1 Temperature resistance up to 80.degree. C.
If the separator fails to meet, or poorly meets, even one of these requirements, significant quality losses or even failure of the electrochemical cell may be the result.
Most often separators of polyamide or polyolefine fibers are employed for the use in storage batteries with an alkaline electrolyte, generally a 30% to 38% aqueous KOH solution.
Generally, untreated, separators of polyphenylene sulfide or polysulfone fibers are poorly wetted by aqueous electrolyte solutions.
From the Patents Abstracts of Japan Vol. 10/No 168 (E-411) Jun. 14th 1986, for Japanese Patent No. JP-A-61-19056, it is known to use area structures of polyolefine, polyvinylalcohol, or polyester that are treated with fluorine-containing nitrogen as separator materials in batteries, especially those with an alkaline electrolyte.
It is also known from the Japanese Patent No. JP-B2-5-46056 to hydrophile synthetic fibers made of polypropylene, polyester or vinylon through a reactive gas of fluorine and oxygen or sulfuric acid. Fibers treated in this manner are used as battery separators that are stable above 45.degree. C.
Fibers or filaments made of polyphenylene sulfide or polysulfone are naturally hydrophobic. With greater wettability through aqueous electrolytes, they would, therefore, be particularly well suited as separator material in electrochemical energy storage devices, because their chemical and thermal resistance makes them resilient to the conditions that occur on the inside of an accumulator.